Now, to the latest on the trial of the utah doctor accused of killing his wife, who was found dead in her bathtub. The jury heard critical testimony from his adult daughter who believes his father is guilty. And the defense grilled her. Tough cross-examine. Aditi roy. Reporter: Alexis somer faced a barrage of questions from his lawyer. Your account in september of 2008 is different than 2011. Reporter: He grilled her for an hour and a half, pointing out discrepancies between her statements. Your descriptions change overtime. I wouldn't necessarily say that. I think in one instance, I was saying she took it off in the bathroom. I was making generalizations there. Reporter: Prosecutors say MacNEILL KILLED HIS WIFE BY Overmedicating her with painkillers. but MacNeill says he is innocent. Your mom was happy. She was feeling a little sick. That's what you said, right? I don't remember her saying she was feeling a little sick. I remember her being up and getting ready for the day. You remembered it on the day of her funeral, right? I don't remember her feeling bad at all. She was feeling great. Reporter: The defense MAINTAINS michele MacNeill died of a heart disorder, which is what the original examiner concluded. But the chief medical examiner amended the cause of death to undetermined. Saying drug toxicity may have played a role, too. And the investigation was reopened. If you learned that the defendant or somebody had told others that he had drugged up michele MacNeill and convinced her to get in the tub and held her down, would that scenario be consistent with how michele MacNEILL DIED HERE? Certainly is possible. Reporter: Testimony resumes today, with fellow inmates of MacNEILL EXPECTED TO TAKE THE Stand. For "good morning america," aditi roy, abc news, los angeles. We're going to turn to legal affairs anchor dan abrams. Alexis' testimony, how did you take it? It's crucial in the context of this case. Particularly in regard to the drugs. That's what this case is about. The prosecutors believe that he set this whole thing up. He orchestrated it, so he could overprescribe her with medication. She's the one talking to her mother. And her mother's questioning, why is he giving me all of the drugs? She even said that the mother hands her some of the drugs and says, look, this is what he's giving me. And most importantly, she said, I leave the house because at that point I feel, okay, mom's all right now. She's recovering. I've been overseeing the recovery. She's fine now. The next thing she knows, her mom is dead. We heard in aditi's report, the defense attorneys really went after her in the cross-examination. In a personal way, as well. Why did you say this one time and this another time? This was, you lied on your medical school application. This was you're a bad person, you're a liar, you're not trustworthy. Why is the defense doing that? They have to. If this jury believes alexis, i don't see how they don't convict. So, she's really important. And the medical examiner. We heard from him, in changing the cause of death. The best hope for the defense in this case is the medical examiner. I think there's a chance, a small chance, but a chance that these jurors could believe, we think he wanted to do it. We think he planned to do it. But we're not sure he was actually able to execute it. We're not convinced beyond a reasonable doubt that there's proof that this was actually a murder. Many will continue to watch. And we're going to have you back. "The jury's out." Looking forward to it.

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